The present invention relates to a method of manufacturing a liquid-crystal display panel, and, more particularly, to a method of manufacturing a so-called active matrix liquid-crystal display panel provided with thin film switching elements which correspond to individual pixels.
The aforesaid liquid-crystal display panel provided with thin film switching elements operates in such a manner that all thin film switching elements corresponding to individual pixels arrayed in a predetermined column of a matrix of pixels are turned on, and voltages corresponding to a video signal are applied to the individual pixels via the thin film switching elements which are turned on.
The thin film switching element consists of an MOS transistor which is obtained by forming an insulator film to cover a semiconductor layer made of, for example, polycrystalline silicon (referred to as poly-Si) formed on a surface of a transparent plate in the shape of islands; forming gate electrodes on the insulator film in such a manner as to divide the semiconductor layer into parts; and forming source regions and drain regions by impurity ion implantation by using the gate electrodes as a mask (self alignment).
In this arrangement, the gate electrodes of the thin film switching elements arrayed in the columns are connected in common to constitute scanning lines, whereas the drain electrodes of the thin film switching elements arrayed in the rows are connected in common to constitute video signal lines.
The source and drain regions in the liquid-crystal display panel described above are formed by impurity ion implantation using the gate electrodes as a mask. As a result, the source and drain regions are formed in such a manner that their opposing ends are positioned immediately under the corresponding sides of the gate electrode in the channel-width direction thereof.
For this reason, if a thin film switching element is turned off, the charge stored in a corresponding pixel electrode will cause an avalanche phenomenon on the drain side of a gate electrode via the gate electrode which has a negative potential with respect to the potential of a source (drain-induced breakdown).
One approach to this problem is to offset the source and drain regions from each gate electrode. However, this approach still has the problem of increasing the number of manufacturing steps.